Carbon is a full suite intended to make Lua more semantic, expressive, and powerful. It aims to provide a set of functionality comparable to .NET, and runs on Lua 5.1 and LuaJIT on any platform. Carbon will take advantage of a few extras if it finds that they're installed, like LuaJIT's FFI, LuaSocket, and LÖVE.
Carbon uses a custom cross-platform loader and namespacing provider, Graphene along with a large set of semantic utility libraries providing object orientation, strong typing facilities, data structure utilities, asynchronous events and I/O, testing, profiling, and math utilities.
You can see Carbon's documentation at http://carbon.lpghatguy.com, which works much better than GitHub's in-tree markdown viewer.
See changes.md for the release and change history of Carbon.